Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods, apparatuses, and non-transitory computer-readable storage mediums for video encoding/decoding. An apparatus includes processing circuitry that decodes prediction information for a current block in a current picture that is a part of a coded video sequence. The prediction information includes a first syntax element indicating whether both quantization parameter (QP) information of a luma component and QP information of a chroma component of the current block are included in the prediction information. The processing circuitry determines a QP of the chroma component based on the QP information of the luma component and the QP information of the chroma component based on the first syntax element indicating that both the QP information of the luma component and the QP information of the chroma component are included in the prediction information. The processing circuitry reconstructs the current block based on the QP of the chroma component.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 63/009,286, “SIGNALING OF CHROMAQUANTIZATION PARAMETERS,” filed on Apr. 13, 2020, U.S. ProvisionalApplication No. 63/029,363, “CHROMA QUANTIZATION PARAMETER MAPPING,”filed on May 22, 2020, and U.S. Provisional Application No. 63/030,060,“ALTERNATIVE METHOD ON CHROMA QUANTIZATION PARAMETER MAPPING,” filed onMay 26, 2020, which are incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar MV derived from MVs of a neighboringarea. That results in the MV found for a given area to be similar or thesame as the MV predicted from the surrounding MVs, and that in turn canbe represented, after entropy coding, in a smaller number of bits thanwhat would be used if coding the MV directly. In some cases, MVprediction can be an example of lossless compression of a signal(namely: the MVs) derived from the original signal (namely: the samplestream). In other cases, MV prediction itself can be lossy, for examplebecause of rounding errors when calculating a predictor from severalsurrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1C, a current block (111) can include samples thathave been found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (112 through 116, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide apparatuses for videoencoding/decoding. An apparatus includes processing circuitry thatdecodes prediction information for a current block in a current picturethat is a part of a coded video sequence. The prediction informationincludes a first syntax element indicating whether both quantizationparameter (QP) information of a luma component and QP information of achroma component of the current block are included in the predictioninformation. The processing circuitry determines a QP of the chromacomponent based on the QP information of the luma component and the QPinformation of the chroma component based on the first syntax elementindicating that both the QP information of the luma component and the QPinformation of the chroma component are included in the predictioninformation. The processing circuitry reconstructs the current blockbased on the QP of the chroma component.

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on the first syntaxelement in the prediction information indicating that both the QPinformation of the luma component and the QP information of the chromacomponent are included in the picture header of the current picture.

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on a second syntaxelement in the prediction information indicating that the currentpicture is not further partitioned.

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on a third syntaxelement in the prediction information indicating that the picture headerof the current picture is included in a slice header of the currentpicture.

In an embodiment, the processing circuitry decodes a fourth syntaxelement in the prediction information indicating whether a QP of theluma component is equal to the QP of the chroma component of the currentblock based on the first syntax element indicating that the QPinformation of the chroma component is not included in the predictioninformation.

In an embodiment, the processing circuitry determines the QP of thechroma component according to a luma-to-chroma QP mapping table based onthe fourth syntax element in the prediction information indicating thatthe QP of the luma component is not equal to the QP of the chromacomponent of the current block.

In an embodiment, the processing circuitry determines the QP of the lumacomponent as the QP of the chroma component based on the fourth syntaxelement indicating that the QP of the luma component is equal to the QPof the chroma component of the current block.

In an embodiment, the luma-to-chroma QP mapping table is included in theprediction information.

Aspects of the disclosure provide methods for video encoding/decoding.In the method, prediction information is decoded for a current block ina current picture that is a part of a coded video sequence. Theprediction information includes a first syntax element indicatingwhether both QP information of a luma component and QP information of achroma component of the current block are included in the predictioninformation. A QP of the chroma component is determined based on the QPinformation of the luma component and the QP information of the chromacomponent based on the first syntax element indicating that both the QPinformation of the luma component and the QP information of the chromacomponent are included in the prediction information. The current blockis reconstructed based on the QP of the chroma component.

Aspects of the disclosure also provide non-transitory computer-readablemediums storing instructions which when executed by a computer for videodecoding cause the computer to perform any one or a combination of themethods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment;

FIG. 8 shows an exemplary flowchart in accordance with an embodiment;

FIG. 9 shows another exemplary flowchart in accordance with anembodiment;

FIG. 10 shows another exemplary flowchart in accordance with anembodiment;

and

FIG. 11 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Decoder and Encoder Systems

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, MVs, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by MVs, available to the motion compensation predictionunit (453) in the form of symbols (421) that can have, for example X, Y,and reference picture components. Motion compensation also can includeinterpolation of sample values as fetched from the reference picturememory (457) when sub-sample exact MVs are in use, MV predictionmechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum MV allowed reference area, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture MVs, block shapes, and so on, that may serve as an appropriateprediction reference for the new pictures. The predictor (535) mayoperate on a sample block-by-pixel block basis to find appropriateprediction references. In some cases, as determined by search resultsobtained by the predictor (535), an input picture may have predictionreferences drawn from multiple reference pictures stored in thereference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most one MVand reference index to predict the sample values of each block.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two MVs and reference indices to predict the sample values of eachblock. Similarly, multiple-predictive pictures can use more than tworeference pictures and associated metadata for the reconstruction of asingle block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a MV. The MV points to thereference block in the reference picture, and can have a third dimensionidentifying the reference picture, in case multiple reference picturesare in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first MV that points to a first reference block in the firstreference picture, and a second MV that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the MV is derived from one or more MVpredictors without the benefit of a coded MV component outside thepredictors. In certain other video coding technologies, a MV componentapplicable to the subject block may be present. In an example, the videoencoder (603) includes other components, such as a mode decision module(not shown) to determine the mode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, MVs, merge mode information), and calculate inter predictionresults (e.g., prediction block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictionblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard such asHEVC. In an example, the entropy encoder (625) is configured to includethe general control data, the selected prediction information (e.g.,intra prediction information or inter prediction information), theresidue information, and other suitable information in the bitstream.Note that, according to the disclosed subject matter, when coding ablock in the merge submode of either inter mode or bi-prediction mode,there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Signaling of Quantization Parameters

In some related examples such as HEVC and VVC, quantization parameters(QPs) in a quantization process may need to be changed within a picture,such as for rate control and perceptual quantization purposes.

In an example such as VVC Draft 8, the QPs can be controlled inhigh-level syntax elements such as a picture parameter set (PPS), apicture header (PH), or a slice header (SH). The QPs can also becontrolled in low-level syntax elements such as a coding block ortransform block level syntax element.

For a QP of a luma block (i.e., luma QP) controlled in high level syntaxelements, an initial value of the luma QP can be signaled in a PPS, anda flag can also be signaled in the PPS to indicate that an offset valueof the luma QP is either signaled in a PH or a SH. Therefore, a luma QPgranularity can be achieved by adding the QP offset to the initial QPvalue.

Table 1 shows exemplary syntax elements related to a luma QP in a PPS.

TABLE 1 pic_parameter_set_rbsp( ) { Descriptor . . .  init_qp_minus26se(v) . . .  no_pic_partition_flag u(1) . . .  qp_delta_info_in_ph_flagu(1) . . . }

In Table 1, a syntax element init_qp_minus26 plus 26 specifies aninitial value of a luma QP (e.g., SliceQpY) for each slice referring tothe PPS. The initial value of the luma QP SliceQpY can be modified at apicture level when a non-zero value of a picture level luma QP offset(e.g., a syntax element ph_qp_delta in Table 2) is decoded or at a slicelevel when a non-zero value of a slice level luma QP offset (e.g., asyntax element slice_qp_delta in Table 3) is decoded. The value of thesyntax element init_qp_minus26 can be in a range of −(26+QpBdOffset) to+37, inclusive. The variable QpBdOffset represents a range offset valuefor luma and chroma QPs.

In Table 1, a syntax element qp_delta_info_in_ph_flag equal to 1specifies that QP delta or offset information of a luma QP is present ina PH syntax structure and not present in slice headers referring to aPPS that does not contain a PH syntax structure. The syntax elementqp_delta_info_in_ph_flag equal to 0 specifies that the QP delta oroffset information of the luma QP is not present in a PH syntaxstructure and may be present in slice headers referring to a PPS thatdoes not contain a PH syntax structure.

Table 2 shows an exemplary syntax element related to a luma QP in a PH.

TABLE 2 picture_header_structure( ) { Descriptor . . .  if(qp_delta_info_in_ph_flag )   ph_qp_delta se(v) . . . }

In Table 2, a syntax element ph_qp_delta specifies a picture level lumaQP offset of a luma QP (e.g., QpY). An initial value of the luma QP canbe used for coding blocks in a picture until modified by a luma QPoffset value (e.g., CuQpDeltaVal) in a coding unit layer. When thesyntax element qp_delta_info_in_ph_flag is equal to 1, the initial valueof the luma QP for all slices of the picture, SliceQpY, can be derivedas follows:

SliceQpY=26+init_qp_minus26+ph_qp_delta  (Eq. 1)

The value of SliceQpY can be in a range of −QpBdOffset to +63,inclusive.

Table 3 shows an exemplary syntax element related to a luma QP in an SH.

TABLE 3 slice_header( ) { Descriptor . . .  if(!qp_delta_info_in_ph_flag )   slice_qp_delta se(v) . . . }

In Table 3, a syntax element slice_qp_delta specifies a slice level lumaQP offset of a luma QP (e.g., QpY). An initial value of the luma QP canbe used for coding blocks in a slice until modified by a luma QP offsetvalue (e.g., CuQpDeltaVal) in a coding unit layer. When the syntaxelement qp_delta_info_in_ph_flag is equal to 0, the initial value of theluma QP for the slice, SliceQpY, can be derived as follows:

SliceQpY=26+init_qp_minus26+slice_qp_delta  (Eq. 2)

The value of SliceQpY can be in a range of −QpBdOffset to +63,inclusive.

In an example such as VVC Draft 8, a QP of a chroma block (i.e., chromaQP) can be derived by adding a chroma QP offset to a correspondingmapped chroma QP value (e.g., QpCb, QpCr, or QpCbCr). The chroma QPoffset can be signaled in both a PPS and an SH but cannot be signaled ina PH.

Table 4 shows exemplary syntax elements related to the chroma QP offsetsin a PPS.

TABLE 4 pic_parameter_set_rbsp( ) { Descriptor . . . pps_chroma_tool_offsets_present_flag u(1)  if(pps_chroma_tool_offsets_present_flag ) {   pps_cb_qp_offset se(v)  pps_cr_qp_offset se(v)   pps_joint_cbcr_qp_offset_present_flag u(1)  if( pps_joint_cbcr_qp_offset_present_flag )   pps_joint_cbcr_qp_offset_value se(v)  pps_slice_chroma_qp_offsets_present_flag u(1)   . . .  } . . . }

In Table 4, a PPS level chroma tool offset present syntax elementpps_chroma_tool_offsets_present_flag equal to 1 specifies that thesyntax elements related to the chroma tool offsets (e.g., syntaxelements pps_cb_qp_offset, pps_cr_qp_offset,pps_joint_cbcr_qp_offset_present_flag, pps_joint_cbcr_qp_offset_value,and pps_slice_chroma_qp_offsets_present_flag) are present in the PPS rawbyte sequence payload (RBSP) syntax structure. The syntax elementpps_chroma_tool_offsets_present_flag equal to 0 specifies that thesyntax elements related to the chroma tool offsets are not present inthe PPS RBSP syntax structure. When a chroma array type syntax elementChromaArrayType (of which more details are in Table 6) is equal to 0,the syntax element pps_chroma_tool_offsets_present_flag can be equal to0.

In Table 4, syntax elements pps_cb_qp_offset and pps_cr_qp_offsetspecify the PPS level chroma QP offsets to a luma QP (e.g., QpY) usedfor deriving the corresponding chroma QPs (e.g., QpCb and QpCr),respectively. The values of the syntax elements pps_cb_qp_offset andpps_cr_qp_offset can be in a range of −12 to +12, inclusive. When thesyntax element ChromaArrayType is equal to 0, the syntax elementspps_cb_qp_offset and pps_cr_qp_offset are not used in a decoding processand decoders can ignore these values. When the syntax elementspps_cb_qp_offset and pps_cr_qp_offset are not present, the values of thesyntax elements pps_cb_qp_offset and pps_cr_qp_offset can be inferred tobe equal to 0.

In Table 4, a PPS level joint CbCr residual coding (JCCR) QP offsetpresent syntax element pps_joint_cbcr_qp_offset_present_flag equal to 1specifies that syntax elements pps_joint_cbcr_qp_offset_value andjoint_cbcr_qp_offset_list[i] are present in the PPS RBSP syntaxstructure. The syntax element pps_joint_cbcr_qp_offset_present_flagequal to 0 specifies that the syntax elementspps_joint_cbcr_qp_offset_value and joint_cbcr_qp_offset_list[i] are notpresent in the PPS RB SP syntax structure. When the syntax elementChromaArrayType is equal to 0 or an SPS level JCCR enabled flagsps_joint_cbcr_enabled_flag is equal to 0, the syntax elementpps_joint_cbcr_qp_offset_present_flag can be equal to 0. When the syntaxelement pps_joint_cbcr_qp_offset_present_flag is not present, the syntaxelement pps_joint_cbcr_qp_offset_present_flag can be inferred to beequal to 0.

In Table 4, the syntax element pps_joint_cbcr_qp_offset_value specifiesa PPS level chroma QP offset to a luma QP (e.g., QpY) used for derivinga chroma QP value of a chroma block in JCCR mode (e.g., QpCbCr). Thevalue of the syntax element pps_joint_cbcr_qp_offset_value can be in arange of −12 to +12, inclusive. When the syntax element ChromaArrayTypeis equal to 0 or the SPS level JCCR enabled flag syntax elementsps_joint_cbcr_enabled_flag is equal to 0, the syntax elementpps_joint_cbcr_qp_offset_value is not used in a decoding process anddecoders can ignore the value of the syntax elementpps_joint_cbcr_qp_offset_value. When the syntax elementpps_joint_cbcr_qp_offset_present_flag is equal to 0, the syntax elementpps_joint_cbcr_qp_offset_value is not present and can be inferred to beequal to 0.

In Table 4, a syntax element pps_slice_chroma_qp_offsets_present_flagequal to 1 specifies that slice level syntax elements related to thechroma QP offsets slice_cb_qp_offset and slice_cr_qp_offset are presentin slice headers. The syntax elementpps_slice_chroma_qp_offsets_present_flag equal to 0 specifies that thesyntax elements slice_cb_qp_offset and slice_cr_qp_offset are notpresent in the slice headers. When the syntax elementpps_slice_chroma_qp_offsets_present_flag is not present or the syntaxelement ChromaArrayType is equal to 0, the syntax elementpps_slice_chroma_qp_offsets_present_flag can be inferred to be equal to0.

Table 5 shows exemplary syntax elements related to the chroma QP offsetsin an HS.

TABLE 5 slice_header( ) { Descriptor . . .  if(pps_slice_chroma_qp_offsets_present_flag ) {   slice_cb_qp_offset se(v)  slice_cr_qp_offset se(v)   if( sps_joint_cbcr_enabled_flag )   slice_joint_cbcr_qp_offset se(v)  } . . . }

In Table 5, a syntax element slice_cb_qp_offset specifies a differenceto be added to the value of the syntax element pps_cb_qp_offset, such asin Table 4, when determining a value of a chroma QP (e.g., QpCb). Avalue of the syntax element slice_cb_qp_offset can be in a range of −12to +12, inclusive. When the syntax element slice_cb_qp_offset is notpresent, the syntax element slice_cb_qp_offset can be inferred to beequal to 0. A sum value of the syntax elements pps_cb_qp_offset andslice_cb_qp_offset (e.g., pps_cb_qp_offset+slice_cb_qp_offset) can be ina range of −12 to +12, inclusive.

In Table 5, a syntax element slice_cr_qp_offset specifies a differenceto be added to the value of the syntax element pps_cr_qp_offset, such asin Table 4, when determining a value of a chroma QP (e.g., QpCr). Avalue of the syntax element slice_cr_qp_offset can be in the range of−12 to +12, inclusive. When the syntax element slice_cr_qp_offset is notpresent, the syntax element slice_cr_qp_offset can be inferred to beequal to 0. A sum value of the syntax elements pps_cr_qp_offset andslice_cr_qp_offset (e.g., pps_cr_qp_offset+slice_cr_qp_offset) can be ina range of −12 to +12, inclusive.

In Table 5, a syntax element slice_joint_cbcr_qp_offset specifies adifference to be added to the value of the syntax elementpps_joint_cbcr_qp_offset_value, such as in Table 4, when determining avalue of a chroma QP (e.g., QpCbCr). A value of the syntax elementslice_joint_cbcr_qp_offset can be in a range of −12 to +12, inclusive.When the syntax element slice_joint_cbcr_qp_offset is not present, thesyntax element slice_joint_cbcr_qp_offset can be inferred to be equal to0. A sum value of the syntax elements pps_joint_cbcr_qp_offset_value andslice_joint_cbcr_qp_offset (e.g.,pps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset) can be in arange of −12 to +12, inclusive.

In an example such as VVC draft 8, the syntax element ChromaArrayTypedepends on a chroma format sampling structure, which is specifiedthrough syntax elements chroma_format_idc and separatecolour_plane_flag.

Table 6 shows exemplary values of the syntax element ChromaArrayType.

TABLE 6 chroma_ separate_colour_ Chroma Chroma- format_idc plane_flagformat ArrayType 0 0 Mono- 0 chrome 1 0 4:2:0 1 2 0 4:2:2 2 3 0 4:4:4 33 1 4:4:4 0

Table 7 shows an exemplary slice header. In Table 7, a syntax elementpicture_header_in_slice_header_flag equal to 1 specifies an SH referringto a PPS contains a PH syntax structure.

TABLE 7 slice_header( ) { Descriptor picture_header_in_slice_header_flag u(1)  if(picture_header_in_slice_header_flag )   picture_header_structure( )  . ..  byte_alignment( ) }

III. Signaling of Chroma Quantization Parameters in a Picture Header

In an example, the chroma QP offsets can be signaled in a PH. Table 8shows exemplary syntax elements related to the chroma QP offsets in aPH.

TABLE 8 Descriptor picture_header_structure( ) { ...  ph_cb_qp_offset se(v)  ph_cr_qp_offset se (v) ... }

In Table 8, syntax elements ph_cb_qp_offset and ph_cr_qp_offset specifythe PH level chroma QP offsets to a luma QP (e.g., QpY) used forderiving the chroma QPs (e.g., QpCb and QpCr), respectively. Values ofthe syntax elements ph_cb_qp_offset and ph_cr_qp_offset can be in arange of −12 to +12, inclusive. When the syntax elements ph_cb_qp_offsetand ph_cr_qp_offset are not present, the values of the syntax elementsph_cb_qp_offset and ph_cr_qp_offset can be inferred to be equal to 0. Asum value of the syntax elements pps_cb_qp_offset such as in Table 4 andph_cb_qp_offset such as in Table 6 (e.g.,pps_cb_qp_offset+ph_cb_qp_offset) can be in a range of −12 to +12,inclusive. A sum value of the syntax elements pps_cr_qp_offset such asin Table 4 and ph_cr_qp_offset such as in Table 6 (e.g.,pps_cr_qp_offset+ph_cr_qp_offset) can be in a range of −12 to +12,inclusive.

In an example, the chroma QP offsets can be conditionally signaled in aPH based on a chroma format (e.g., a chroma color format or the syntaxelement ChromaArrayType in Table 6). When the syntax elementChromaArrayType is not equal to 0, the syntax elements ph_cb_qp_offsetand ph_cr_qp_offset can be signaled. When there is no chroma componentin a bitstream, the syntax elements ph_cb_qp_offset and ph_cr_qp_offsetare not signaled.

Table 9 shows exemplary syntax elements related to the chroma QP offsetsin a PH based on the syntax element ChromaArrayType.

TABLE 9 Descriptor picture_header_structure( ) { ...  if(ChromaArrayType !=0) {   ph_cb_qp_offset se (v)   ph_cr_qp_offset se(v) ...  } ... }

In Table 9, the syntax elements ph_cb_qp_offset and ph_cr_qp_offsetspecify the PH level chroma QP offsets to a luma QP (e.g., QpY) used forderiving the chroma QPs (e.g, QpCb and QpCr), respectively. The valuesof the syntax elements ph_cb_qp_offset and ph_cr_qp_offset can be in arange of −12 to +12, inclusive. When the syntax elements ph_cb_qp_offsetand ph_cr_qp_offset are not present, the values of the syntax elementsph_cb_qp_offset and ph_cr_qp_offset can be inferred to be equal to 0. Asum value of the syntax elements pps_cb_qp_offset and ph_cb_qp_offset(e.g., pps_cb_qp_offset+ph_cb_qp_offset) can be in a range of −12 to+12, inclusive. A sum value of the syntax elements pps_cr_qp_offset andph_cr_qp_offset (e.g., pps_cr_qp_offset+ph_cr_qp_offset) can be in arange of −12 to +12, inclusive.

In an example, the chroma QP offsets can be signaled in both a PH and anSH to derive the chroma QP values in order to achieve different levelsof a chroma QP granularity. For example, the chroma QP values can bederived based on the signaled chroma QP offset as follows:

QpCb=Clip3(−QpBdOffset,63,QpCb+pps_cb_qp_offset+ph_cb_qp_offset+slice_cb_qp_offset+CuQpOffsetCb)+QpBdOffset  (Eq.3)

QpCr=Clip3(−QpBdOffset,63,QpCr+pps_cr_qp_offset+ph_cr_qp_offset+slice_cr_qp_offset+CuQpOffsetCr)+QpBdOffset  (Eq.4)

In an example, a flag (e.g., a syntax elementchroma_qp_offset_info_in_ph_flag in Table 10) can be signaled toindicate that the chroma QP offsets is signaled in either a PH or an SH.The flag can also be used to condition the QP offset values. The flagcan be signaled in a PPS.

Table 10 shows an exemplary flag indicating the chroma QP offsets aresignaled in either a PH or an SH.

TABLE 10 Descriptor pic_pararneter_set_rbsp( ) { ... pps_chroma_tool_offsets_present_flag u (1)  if(pps_chroma_tool_offsets_present_flag ) { ...  chroma_qp_offset_info_in_philag u (1) ...  } ... }

In Table 10, the syntax element chroma_qp_offset_info_in_ph_flag equalto 1 specifies that the chroma QP offset information is present in a PHsyntax structure and not present in slice headers referring to a PPSthat does not contain a PH syntax structure. The syntax elementchroma_qp_offset_info_in_ph_flag equal to 0 specifies that the chroma QPoffset information is not present in a PH syntax structure and may bepresent in slice headers referring to a PPS that does not contain a PHsyntax structure. When the syntax elementchroma_qp_offset_info_in_ph_flag is not present, the syntax elementchroma_qp_offset_info_in_ph_flag can be inferred to be equal to 0.

Table 11 shows exemplary syntax elements related to the chroma QPoffsets in a PH based on the syntax elementchroma_qp_offset_info_in_ph_flag.

TABLE 11 Descriptor picture_header_structure( ) { ...  if(ChromaArrayType !=0) {   if ( chroma_qp_offset_info_in_ph_flag) {   ph_cb_qp_offset se (v)    ph_cr_qp_offset se (v)   }  } ... }

In Table 11, the syntax element chroma_qp_offset_info_in_ph_flag equalto 1 specifies that the syntax elements ph_cb_qp_offset andph_cr_qp_offset are present in a PH syntax structure and not present inslices headers referring to a PPS that does not contain a PH syntaxstructure. The syntax element chroma_qp_offset_info_in_ph_flag equal to0 specifies that the syntax elements ph_cb_qp_offset and ph_cr_qp_offsetare not present in a PH syntax structure and may be present in sliceheaders referring to a PPS that does not contain a PH syntax structure.

In Table 11, the syntax elements ph_cb_qp_offset and ph_cr_qp_offsetspecify the PH level chroma QP offsets to a luma QP (e.g., QpY) used forderiving the chroma QPs (e.g., QpCb and QpCr), respectively. The valuesof the syntax elements ph_cb_qp_offset and ph_cr_qp_offset can be in arange of −12 to +12, inclusive. When the syntax elements ph_cb_qp_offsetand ph_cr_qp_offset are not present, the values of the syntax elementsph_cb_qp_offset and ph_cr_qp_offset can be inferred to be equal to 0. Asum value of the syntax elements pps_cb_qp_offset and ph_cb_qp_offset(e.g., pps_ch_qp_offset+ph_cb_qp_offset) can be in a range of −12 to+12, inclusive. A sum value of the syntax elements pps_cr_qp_offset andph_cr_qp_offset (e.g., pps_cr_qp_offset+ph_cr_qp_offset) can be in arange of −12 to +12, inclusive.

Table 12 shows exemplary syntax elements related to the chroma QPoffsets in an SH based on the syntax elementchroma_qp_offset_info_in_ph_flag.

TABLE 12 Descriptor slice_header( ) { ...  if (ChromaArrayType !=0) {  if ( !chroma_qp_offset_info_in_ph_flag) {    slice_cb_qp_offset se (v)   slice_cr_qp_offset se (v)   }  } ... }

In Table 12, the syntax element chroma_qp_offset_info_in_ph_flag equalto 0 specifies that the syntax elements slice_cb_qp_offset andslice_cr_qp_offset are present in slice headers referring to a PPS thatdoes not contain a PH syntax structure. When the syntax elementchroma_qp_offset_info_in_ph_flag is not present or the syntax elementChromaArrayType is equal to 0, the syntax elementchroma_qp_offset_info_in_ph_flag can be inferred to be equal to 0.

In an example, the chroma QP offset can be signaled in either a PH or anSH to derive the chroma QP values to achieve different levels of a QPgranularity. For example, the chroma QP values can be derived asfollows:

QpCb=Clip3(−QpBdOffset,63,QpCb+pps_cb_qp_offset+(chroma_qp_offset_info_in_ph_flag?ph_cb_qp_offset:slice_cb_qp_offset)+CuQpOffsetCb)+QpBdOffset  (Eq.5)

QpCr=Clip3(−QpBdOffset,63,QpCr+pps_cr_qp_offset+(chroma_qp_offset_info_in_ph_flag?ph_cr_qp_offset:slice_cr_qp_offset)+CuQpOffsetCr)+QpBdOffset  (Eq.6)

In (Eq. 5) and (Eq. 6), depending on the value of the syntax elementchroma_qp_offset_info_in_ph_flag, only one chroma QP offset for eachequation can be used to derive the corresponding chroma QP value.

In an example, a chroma QP offset of a chroma block in JCCR mode can besignaled in a PH.

Table 13 shows an exemplary syntax element related to a chroma QP offsetfor a chroma block in JCCR mode in a PH.

TABLE 13 Descriptor picture_header_structure( ) { ... ph_joint_cbcr_qp_offset se (v) ... }

In Table 13, a syntax element ph_joint_cbcr_qp_offset specifies a chromaQP offset to a luma QP (e.g., QpY) used for deriving a chroma QP valueof a chroma block in JCCR mode (e.g., QpCbCr). A value of the syntaxelement ph_joint_cbcr_qp_offset can be in a range of −12 to +12,inclusive. When the syntax element ph_joint_cbcr_qp_offset is notpresent, the value of the syntax element ph_joint_cbcr_qp_offset can beinferred to be equal to 0. A sum value of the syntax elementspps_joint_cbcr_qp_offset_value in Table 4 and ph_joint_cbcr_qp_offset(e.g., pps_joint_cbcr_qp_offset_value+ph_joint_cbcr_qp_offset) can be ina range of −12 to +12, inclusive.

In an example, a chroma QP offset of a chroma block in JCCR mode can beconditionally signaled in a PH based on a chroma format (e.g., a chromacolor format or the syntax element ChromaArrayType).

Table 14 shows an exemplary syntax element related to a chroma QP offsetfor a chroma block in JCCR mode in a PH based on the syntax elementChromaArrayType.

TABLE 14 Descriptor picture_header_structure( ) { ...  if(ChromaArrayType !=0) {   ph_joint_cbcr_qp_offset se (v) ...  } ... }

In Table 14, when the syntax element ChromaArrayType is not equal to 0,the syntax element ph_joint_cbcr_qp_offset can be signaled in the PH.When there is no chroma component in a bitstream, the syntax elementph_joint_cbcr_qp_offset is not signaled. The syntax elementph_joint_cbcr_qp_offset specifies a PH level chroma QP offset to a lumaQP (e.g., QpY) used for deriving a chroma QP value of a chroma block inJCCR mode (e.g, QpCbCr). A value of the syntax elementph_joint_cbcr_qp_offset can be in a range of −12 to +12, inclusive. Whenthe syntax element ph_joint_cbcr_qp_offset is not present, the value ofthe syntax element ph_joint_cbcr_qp_offset can be inferred to be equalto 0. A sum value of the syntax elements pps_joint_cbcr_qp_offset_valuein Table 4 and ph_joint_cbcr_qp_offset (e.g.,pps_joint_cbcr_qp_offset_value+ph_joint_cbcr_qp_offset) can be in arange of −12 to +12, inclusive.

In an example, a chroma QP offset of a chroma block in JCCR mode can besignaled in both a PH and an SH to derive a chroma QP value of thechroma block in JCCR mode in order to achieve different levels of agranularity of the chroma QP. For example, the chroma QP value of thechroma block in JCCR mode can be derived as follow:

QpCbCr=Clip3(−QpBdOffset,63,QpCbCr+pps_joint_cbcr_qp_offset_value+ph_joint_cbcr_qp_offset+slice_joint_cbcr_qp_offset+CuQpOffsetCbCr)+QpBdOffset  (Eq.7)

In an example, a flag (e.g., the syntax elementchroma_qp_offset_info_in_ph_flag in Table 10) can be signaled toindicate that a chroma QP offset of a chroma block in JCCR mode can besignaled in either a PH or an SH. The flag can also be used to conditionthe chroma QP offset value.

Table 15 shows exemplary syntax elements related to the chroma QPoffsets in a PH based on the syntax elementchroma_qp_offset_info_in_ph_flag.

TABLE 15 Descriptor picture_header_structure( ) { ...  if(ChromaArrayType !=0) (   if ( chroma_qp_offset_info_in_ph_flag) {   ph_cb_qp_offset se (v)    ph_cr_qp_offset se (v)   ph_joint_cbcr_qp_offset se (v) ...   }  } ... }

In Table 15, the syntax element chroma_qp_offset_info_in_ph_flag equalto 1 specifies that the PH level syntax elements related to the chromaQP offsets ph_cb_qp_offset, ph_cr_qp_offset, and ph_joint_cbcr_qp_offsetare present in a PH syntax structure and not present in slices headersreferring to a PPS that does not contain the PH syntax structure. Thesyntax element chroma_qp_offset_info_in_ph_flag equal to 0 specifiesthat the syntax elements ph_cb_qp_offset, ph_cr_qp_offset, andph_joint_cbcr_qp_offset are not present in a PH syntax structure and maybe present in slice headers referring to a PPS that does not contain aPH syntax structure.

In Table 15, the syntax element ph_joint_cbcr_qp_offset specify a chromaQP offset to a luma QP (e.g., QpY) used for deriving a chroma QP valueof a chroma block in JCCR mode (e.g., QpCbCr). The value of the syntaxelement ph_joint_cbcr_qp_offset can be in a range of −12 to +12,inclusive. When the syntax element ph_joint_cbcr_qp_offset is notpresent, the values of the syntax element ph_joint_cbcr_qp_offset can beinferred to be equal to 0. A sum value of the syntax elementspps_joint_cbcr_qp_offset_value in Table 4 and ph_joint_cbcr_qp_offset(e.g., pps_joint_cbcr_qp_offset_value+ph_joint_cbcr_qp_offset) can be ina range of −12 to +12, inclusive.

Table 16 shows exemplary syntax elements related to the chroma QPoffsets in an SH based on the syntax elementchroma_qp_offset_info_in_ph_flag.

TABLE 16 Descriptor slice_header( ) { ...  if (ChromaArrayType !=0) {  if ( !chroma_qp_offset_info_in_ph_flag) {    slice_cb_qp_offset se (v)   slice_cr_qp_offset se (v)    slice_joint_cbcr_qp_offset se (v) ...  }  } ... }

In Table 16, the syntax element chroma_qp_offset_info_in_ph_flag equalto 0 specifies that the slice level syntax elements related to thechroma QP offsets slice_cb_qp_offset, slice_cr_qp_offset, andslice_joint_cbcr_qp_offset are present in an SH syntax structurereferring to a PPS that does not contain a PH syntax structure and notpresent in a PH. The syntax element chroma_qp_offset_info_in_ph_flagequal to 1 specifies that the syntax elements slice_cb_qp_offset,slice_cr_qp_offset, and slice_joint_cbcr_qp_offset are not present inthe SH syntax structure referring to a PPS that does not contain a PHsyntax structure and may be present in a PH syntax structure.

In Table 16, the syntax element slice_joint_cbcr_qp_offset specify achroma QP offset to a luma QP (e.g., QpY) used for deriving a chroma QPvalue of a chroma block in JCCR mode (e.g., QpCbCr). The value of thesyntax element slice_joint_cbcr_qp_offset can be in a range of −12 to+12, inclusive. When the syntax element slice_joint_cbcr_qp_offset isnot present, the values of the syntax element slice_joint_cbcr_qp_offsetcan be inferred to be equal to 0. A sum value of the syntax elementspps_joint_cbcr_qp_offset_value such as in Table 4 andslice_joint_cbcr_qp_offset (e.g.,pps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset) can be in arange of −12 to +12, inclusive.

In an example, the chroma QP value can be derived as follows:

QpCbCr=Clip3(−QpBdOffset,63,QpCbCr+pps_joint_cbcr_qp_offset_value+(chroma_qp_offset_info_in_ph_flag?ph_joint_cbcr_qp_offset:slice_joint_cbcr_qp_offset)+CuQpOffsetCbCr)+QpBdOffset  (Eq.8)

In (Eq. 8), depending on the value of the syntax elementchroma_qp_offset_info_in_ph_flag, only one chroma QP offset can be usedto derive the chroma QP value of the chroma block in JCCR mode.

IV. Signaling of Chroma Quantization Parameters

This disclosure includes embodiments directed to signaling of chroma QPinformation. According to some embodiments in this disclosure, thechroma QP information can be signaled in a PH without encoding/decodingsome syntax elements related to chroma QP offsets such as the syntaxelement chroma_qp_offset_info_in_ph_flag in Table 10.

In an embodiment, a syntax element in a PPS can be used to indicatewhere a global QP offset is signaled, for example whether the global QPoffset is signaled in a PH or SH. An existing syntax elementqp_delta_info_in_ph_flag such as in Table 1, which indicates whether theglobal luma QP offset is signaled in the PH or the SH, can be used toindicate whether the global chroma QP offset is signaled in the PH orthe SH. The flag can also be used to condition the QP offset value.

Table 17 shows exemplary syntax elements related to chroma QP offsetsbased on the syntax element qp_delta_info_in_ph_flag.

TABLE 17 Descriptor picture_header_structure( ) { ...  if(ChromaArrayType !=0) {   if (qp_delta_info_in_ph_flag) {   ph_cb_qp_offset se (v)    ph_cr_qp_offset se (v)   ph_joint_cbcr_qp_offset se (v)   }  } ... }

In Table 17, the syntax element qp_delta_info_in_ph_flag equal to 1specifies that both luma and chroma QP offset information are present ina PH syntax structure and not present in slice headers referring to aPPS that does not contain a PH syntax structure. The syntax elementqp_delta_info_in_ph_flag equal to 0 specifies that both the luma andchroma QP offset information are not present in a PH syntax structureand may be present in slice headers referring to the PPS that does notcontain a PH syntax structure.

In an embodiment, when a flag indicates a current picture is not furtherpartitioned (e.g., when a syntax element no_pic_partition_flag in Table1 is equal to 1), the syntax element chroma_qp_offset_info_in_ph_flag inTable 10 may not be signaled.

Table 18 shows an exemplary syntax element related to the chroma QPoffset based on the syntax element no_pic_partition_flag.

TABLE 18 Descriptor pic_parameter_set_rbsp( ) { ... pps_chroma_tool_offsets_present_flag u (1)  if(pps_chroma_tool_offsets_present_flag ) { ...    if(!no_pic_partition_flag)     chroma_qp_offset_info_in_ph_flag u (1) ... } ... }

In Table 18, the syntax element no_pic_partition_flag equal to 1specifies that a current picture is not further partitioned and thusincludes only one slice. The syntax element no_pic_partition_flag equalto 0 specifies that the current picture can be further partitioned andthus includes more than one slice. When the syntax elementno_pic_partition_flag is equal to 1, a syntax elementchroma_qp_offset_info_in_ph_flag is not signaled. In an embodiment, whenthe syntax element chroma_qp_offset_info_in_ph_flag is not present, avalue of the syntax element chroma_qp_offset_info_in_ph_flag can beinferred to be equal to 1. Therefore, the global chroma QP offsets in aPH can be used for the derivation of the chroma QP values.

In an embodiment, when a flag indicates that a picture header of acurrent picture is included in a slice header of the current picture(e.g., when the syntax element picture_header_in_slice_header_flag inTable 7 is equal to 1), a syntax elementchroma_qp_offset_info_in_ph_flag can be equal to 1. The syntax elementchroma_qp_offset_info_in_ph_flag equal to 1 specifies that the chroma QPoffset information is present in a PH syntax structure and not presentin slice headers referring to a PPS that does not contain a PH syntaxstructure. The syntax element chroma_qp_offset_info_in_ph_flag equal to0 specifies that the QP offset information is not present in a PH syntaxstructure and may be present in slice headers referring to a PPS thatdoes not contain a PH syntax structure. When the syntax elementchroma_qp_offset_info_in_ph_flag is not present, a value of the syntaxelement chroma_qp_offset_info_in_ph_flag can be inferred to be equal to0. When slice headers referring to the PPS contain a PH syntax structure(e.g., when the syntax element picture_header_in_slice_header_flag isequal to 1), it is a requirement of a bitstream conformance that thesyntax element chroma_qp_offset_info_in_ph_flag can be equal to 1.

V. Chroma Quantization Parameters Mapping

In some related examples such as HEVC, if a chroma format is 4:2:0, afixed look-up table can be used for both chroma QPs QpCb and QpCr toconvert a luma QP QpY to the chroma QPs, QpCb, and QpCr. Otherwise, thechroma QP QpCb and QpCr can be set equal to a minimum value between QpYand 51.

In an example such as VVC Draft 9, a more flexible luma-to-chroma QPmapping is used. Instead of a fixed table, the luma-to-chroma QP mappingrelationship is signaled in an SPS using a flexible piecewise linearmodel. A constraint of the piecewise linear model is that a slope ofeach piece cannot be negative. That is, as the luma QP increases, thechroma QP either stays flat or increases, but cannot decrease. Thepiecewise linear model can be defined by: (i) number of pieces in themodel and (ii) input (luma) and output (chroma) delta QPs for eachpiece. The QP mapping relationship can be signaled separately for Cb,Cr, and joint CbCr residual coding, or signaled once and used for allthree types of residual coding.

It is noted that, unlike HEVC, the luma-to-chroma QP mapping in VVC canbe used for the chroma formats of 4:2:0, 4:2:2, and 4:4:4. That is, forthese chroma formats, the syntax elements related to the luma-to-chromaQP mapping can be signaled.

Table 19 shows exemplary syntax elements related to the luma-to-chromaQP mapping signaled in an SPS.

TABLE 19 Descriptor seq_parameter_set_rbsp( ) ( ...  if( ChromaArrayType!= 0) {   sps joint_cbcr_enabled_flag u (1)  sps_same_qp_table_for_chroma_flag u (1)   numQpTABLEs =sps_same_qp_table_for chroma_flag ? 1:     ( sps_joint_cbcr_enabled_flag? 3 : 2)   for( i = 0; i < numQpTABLEs; i++ ) {   sps_qp_table_start_minus26[ i ] se (v)   sps_num_points_in_qp_table_minus1[ i ] ue (v)    for( j = 0; j <=sps_num_points_in_qp_table_minus1[ i ]; j++) {    sps_delta_qp_in_val_minus1[ i ][ j ] ue (v)    sps_delta_qp_diff_val[ i ][ j ] ue (v)    }   }  } ... }

In Table 19, a syntax element sps_same_qp_table_for_chroma_flag equal to1 specifies that only one luma-to-chroma QP mapping table is signaledand this table can apply to both Cb and Cr residuals and additionally tojoint CbCr residuals when the SPS level JCCR enabled flagsps_joint_cbcr_enabled_flag is equal to 1. The syntax elementsps_same_qp_table_for_chroma_flag equal to 0 specifies that theluma-to-chroma QP mapping tables, two for Cb and Cr, and one additionalfor joint CbCr when the syntax element sps_joint_cbcr_enabled_flag isequal to 1, are signaled in the SPS. When the syntax elementsps_same_qp_table_for_chroma_flag is not present, a value of the syntaxelement sps_same_qp_table_for_chroma_flag can be inferred to be equal to1.

In Table 19, a syntax element sps_qp_table_start_minus26[i] plus 26specifies the starting luma and chroma QPs used to describe an i-thluma-to-chroma QP mapping table. A value of the syntax elementsps_qp_table_start_minus26[i] can be in a range of −26-QpBdOffset to 36,inclusive. When the syntax element sps_qp_table_start_minus26[i] is notpresent, the value of the syntax element sps_qp_table_start_minus26[i]can be inferred to be equal to 0.

In Table 19, a syntax element sps_num_points_in_qp_table_minus1[i] plus1 specifies the number of points used to describe the i-thluma-to-chroma QP mapping table. A value of the syntax elementsps_num_points_in_qp_table_minus1[i] can be in a range of 0 to63+QpBdOffset, inclusive. When the syntax elementsps_num_points_in_qp_table_minus1[i] is not present, the value of thesyntax element sps_num_points_in_qp_table_minus1[0] can be inferred tobe equal to 0.

In Table 19, a syntax element sps_delta_qp_in_val_minus1[i][j] specifiesa delta value used to derive an input coordinate of a j-th pivot pointof the i-th luma-to-chroma QP mapping table. When the syntax elementsps_delta_qp_in_val_minus1[0][j] is not present, a value of the syntaxelement sps_delta_qp_in_val_minus1[0][j] can be inferred to be equal to0.

In Table 19, a syntax element sps_delta_qp_diff_val[i][j] specifies adelta value used to derive an output coordinate of the j-th pivot pointof the i-th luma-to-chroma QP mapping table.

The value of the luma and chroma QP range offset is QpBdOffset.

In an example, the i-th luma-to-chroma QP mapping table ChromaQpTable[i]for i=0 . . . numQpTables−1 can be derived in Table 20.

TABLE 20 qpInVal[ i ][ 0 ] = sps_qp_table_start_minus26[ i ] + 26qpOutVal[ i ][ 0 ] = qpInVal[ i ][ 0 ] for( j = 0; j <=sps_num_points_in_qp_table_minus1[ i ]; j++ ) {  qpInVal[ i ][ j + 1 ] =qpInVal[ i ][ j ] + sps_delta_qp_in_val_minus1[ i ][ j ] +1  qpOutVal[ i][ j + 1 ] =qpOutVal[ i ][ j ] +( sps_delta_qp_in_val_minus1[ i ][ j]^(∧) sps_delta_qp_diff_val[ i ][ j ] ) } ChromaQpTABLE[ i ][ qpInVal[ i][ 0 ] ] = qpOutVal[ i ][ 0 ] for ( k = qpInVal[ i ][ 0 ] − 1; k >=−QpBdOffset; k −− )  ChromaQpTABLE[ i ][ k ] = Clip3 ( −QpBdOffset, 63,ChromaQpTABLE[ i ][ k + 1 ] − 1 ) for ( j = 0; j <=sps_num_points_in_qp_table_minus1[ i ]; j++ ) {  sh = (sps_delta_qp_in_val_minus1[ i ][ j ] + 1 ) >> 1  for ( k = qpInVal[ i ][j ] + 1, m = 1; k <= qpInval[ i ][ j +1 ]; k++, m++ )   ChromaQpTABLE[ i][ k ] = ChromaQpTABLE[ i ][ qpInVal[ i ][ j ] ] + ( ( qpOutVal[ i ][ j+1 ] − qpOutVal[ i ][ j ] ) * m + sh ) / ( sps_delta_qp_in_val_minus1[ i][ j ] + 1 ) } for ( k = qpInVal[ i ][sps_num_points_in_qp_table_minus1[ i ] + 1 ] + 1; k <= 63; k++ ) ChromaQpTABLE[ i ][ k ] = Clip3 ( −QpBdOffset, 63, ChromaQpTABLE[ i ][k − 1 ] + 1 )

In Table 20, when a syntax element sps_same_qp_table_for_chroma_flag isequal to 1, the syntax elements ChromaQpTable[1][k] andChromaQpTable[2][k] are set equal to ChromaQpTable[0][k] for kin a rangeof −QpBdOffset to 63, inclusive.

It is a requirement of a bitstream conformance that values of the syntaxelements qpInVal[i][j] and qpOutVal[i][j] can be in a range of−QpBdOffset to 63, inclusive for i in a range of 0 to numQpTables−1,inclusive, and j in a range of 0 tosps_num_points_in_qp_table_minus1[i]+1, inclusive.

However, when the syntax element sps_num_points_in_qp_table_minus1[i]for i-th luma-to-chroma QP mapping table has a value equal to63+QpBdOffset, the syntax element qpInVal[i][63+QpBdOffset+1] has avalue exceeding a maximum QP value (e.g., 63).

As described above, the design of the luma-to-chroma QP mapping maycause the QP value to exceed the maximum QP value (e.g., 63) in somecases. In addition, for a chroma format that is not 4:2:0, the chromaQPs QpCb and QpCr can be set equal to the luma QP QpY (e.g., for 4:4:4).

This disclosure includes embodiments directed to the luma-to-chroma QPmapping.

In an embodiment, the range of the syntax elements related to theluma-to-chroma QP mapping is limited such that the chroma QP values donot exceed the maximum QP value. For example, the range of the syntaxelement sps_num_points_in_qp_table_minus1[i] is constrained in a rangeof 0 to (63+QpBdOffset−1), inclusive. With such a constraint, when thesyntax element sps_num_points_in_qp_table_minus1[i] is equal to63+QpBdOffset−1 for the i-th luma-to-chroma QP mapping table, the syntaxelement qpInVal[i][63+QpBdOffset] does not exceed the maximum QP value63.

In an embodiment, the luma-to-chroma QP mapping derivation can besimplified for the case in which the chroma QPs QpCb and QpCr are setequal to the luma QP QpY.

Table 21 shows exemplary syntax elements required to derive aluma-to-chroma QP mapping table and their ranges in worst case.

TABLE 21 Syntax element Range of value in worst casesps_same_qp_table_for_chroma_flag 0 to 1 sps_qp_table_start_minus26[ i ]−74 to 36  sps_num_points_in_qp_table_minus1[ i ]  0 to 111

In an embodiment, to derive the luma-to-chroma QP mapping table in whichthe chroma QPs QpCb and QpCr are set equal to the luma QP QpY, a syntaxelement (e.g., sps_chroma_qp_identical_to_luma_flag in Table 22) can besignaled to indicate whether the syntax elements related to theluma-to-chroma QP mapping are signaled.

Table 22 shows an exemplary syntax element indicating whether the syntaxelements related to the luma-to-chroma QP mapping are signaled.

TABLE 22 Descriptor seq_parameter_set_rbsp ( ) { ...  if (ChromaAtTayType != 0) {   sps_joint_cbcr_enabledilag u (1)  sps_chroma_qp_identical_to_luma_flag u (1)   if(sps_chroma_qp_identical_to_luma_flag != 1) {    sps_same_qp_table_for_chroma_flag u (1)     numQpTABLEs =sps_same_qp_table_for_chroma_flag ? 1:      (sps_joint_cbcr_enabled_flag ? 3 : 2)    for ( i = 0; i < numQpTABLEs;i++ ) {     sps_qp_table_start_minus26[ i ] se (v)    sps_num_points_in_qp_table_minus1[ i ] ue (v)     for ( j = 0; j <=sps_num_points_in_qp_table_minus1[ i ]; j++) {     sps_delta_qp_in_val_minus1[ i ][ j ] ue (v)     sps_delta_qp_diff_val[ i ][ j ] ue (v)     }    }   }  } ... }

In Table 22, a syntax element sps_chroma_qp_identical_to_luma_flag equalto 1 specifies that each chroma QP has an identical value with that ofthe luma QP and thus the syntax elements related to the luma-to-chromaQP mapping are not signaled. The syntax elementsps_chroma_qp_identical_to_luma_flag equal to 0 specifies that thechroma QP does not have the identical value with that of luma QP andthus the syntax elements related to the luma-to-chroma QP mapping may besignaled. When the syntax element sps_chroma_qp_identical_to_luma_flagis not present, the value of the syntax elementsps_chroma_qp_identical_to_luma_flag can be inferred to be equal to 1.

In Table 22, a syntax element sps_delta_qp_diff_val[i][j] specifies adelta value used to derive an output coordinate of a j-th pivot point ofan i-th luma-to-chroma QP mapping table. When the syntax elementsps_chroma_qp_identical_to_luma_flag equals to 1, the value of thesyntax element sps_delta_qp_diff_val[i][j] can be inferred to be equalto 1.

VII. Flowchart

FIG. 8 shows a flow chart outlining an exemplary process (800) accordingto an embodiment of the disclosure. In various embodiments, the process(800) is executed by processing circuitry, such as the processingcircuitry in the terminal devices (210), (220), (230) and (240), theprocessing circuitry that performs functions of the video encoder (303),the processing circuitry that performs functions of the video decoder(310), the processing circuitry that performs functions of the videodecoder (410), the processing circuitry that performs functions of theintra prediction module (452), the processing circuitry that performsfunctions of the video encoder (503), the processing circuitry thatperforms functions of the predictor (535), the processing circuitry thatperforms functions of the intra encoder (622), the processing circuitrythat performs functions of the intra decoder (772), and the like. Insome embodiments, the process (800) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (800).

The process (800) may generally start at step (S810), where the process(800) decodes prediction information for a current block in a currentpicture that is a part of a coded video sequence. The predictioninformation includes a first syntax element indicating whether both QPinformation of a luma component and QP information of a chroma componentof the current block are included in the prediction information. Whenthe first syntax element indicates that both the QP information of theluma component and the QP information of the chroma component areincluded in the prediction information, the process (800) proceeds tostep (S820). Otherwise, the process (800) proceeds to step (S830).

At step (S820), the process (800) determines a QP of the chromacomponent based on the QP information of the luma component and the QPinformation of the chroma component included in the predictioninformation. Then, the process (800) proceeds to step (S860).

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on the first syntaxelement in the prediction information indicating that both the QPinformation of the luma component and the QP information of the chromacomponent are included in the picture header of the current picture.

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on a second syntaxelement in the prediction information indicating that the currentpicture is not further partitioned.

In an embodiment, the QP information of the chroma component is includedin a picture header of the current picture based on a third syntaxelement in the prediction information indicating that the picture headerof the current picture is included in a slice header of the currentpicture.

At step (S830), the process (800) decodes a fourth syntax element in theprediction information indicating whether a QP of the luma component isequal to the QP of the chroma component of the current block. When thefourth syntax element in the prediction information indicates that theQP of the luma component is equal to the QP of the chroma component ofthe current block, the process (800) proceeds to step (S840). Otherwise,the process (800) proceeds to step (S850).

At step (S840), the process (800) determines the QP of the lumacomponent as the QP of the chroma component. Then, the process (800)proceeds to step (S860).

At step (S850), the process (800) determines the QP of the chromacomponent based on a luma-to-chroma QP mapping table. Then, the process(800) proceeds to step (S860).

In an embodiment, the luma-to-chroma QP mapping table is included in theprediction information.

At step (S860), the process (800) reconstructs the current block basedon the QP of the chroma component. Then, the process (800) terminates.

While syntax elements have been described in the disclosure usingcertain values, it is noted that the values are merely exemplary. One ormore of the syntax elements can use other values to signal the sameinformation.

FIG. 9 shows another flow chart outlining an exemplary process (900)according to an embodiment of the disclosure. In various embodiments,the process (900) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (900) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(900).

The process (900) may generally start at step (S910), where the process(900) decodes prediction information for a current block in a currentpicture that is a part of a coded video sequence. The predictioninformation includes a syntax element indicating whether both QPinformation of a luma component and QP information of a chroma componentof the current block are included in the prediction information. Then,the process (900) proceeds to step (S920).

At step (S920), the process (900) determines a QP of the chromacomponent based on the syntax element indicating that both the QPinformation of the luma component and the QP information of the chromacomponent of the current block are included in the predictioninformation. In an embodiment, the syntax element indicates that boththe QP information of the luma component and the QP information of thechroma component of the current block are included in a PH syntaxstructure, and the process (900) determines the QP of the chromacomponent based on the QP information of the luma component and the QPinformation of the chroma component in the PH syntax structure. Then,the process (900) proceeds to step (S930).

At step (S930), the process (900) reconstructs the current block basedon the QP of the chroma component. Then, the process (900) terminates.

FIG. 10 shows another flow chart outlining an exemplary process (1000)according to an embodiment of the disclosure. In various embodiments,the process (1000) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1000) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1000).

The process (1000) may generally start at step (S1010), where theprocess (1000) decodes prediction information for a current block in acurrent picture that is a part of a coded video sequence. The predictioninformation includes a syntax element indicating whether a QP of a lumacomponent is equal to a QP of a chroma component of the current block.When the syntax element indicates that the QP of the luma component isequal to the QP of the chroma component of the current block, theprocess (1000) proceeds to step (S1020). Otherwise, the process (1000)proceeds to step (S1030).

At step (S1020), the process (1000) determines the QP of the lumacomponent as the QP of the chroma component. Then, the process (1000)proceeds to step (S1040).

At step (S1030), the process (1000) determines the QP of the chromacomponent based on a luma-to-chroma QP mapping table. Then, the process(1000) proceeds to step (S1040).

At step (S1040), the process (1000) reconstructs the current block basedon the QP of the chroma component.

VIII. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 11 shows a computersystem (1100) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 11 for computer system (1100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1100).

Computer system (1100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data-glove (not shown), joystick (1105), microphone(1106), scanner (1107), and camera (1108).

Computer system (1100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1110), data-glove (not shown), or joystick (1105), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1109), headphones(not depicted)), visual output devices (such as screens (1110) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted). These visual output devices (such as screens(1110)) can be connected to a system bus (1148) through a graphicsadapter (1150).

Computer system (1100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1120) with CD/DVD or the like media (1121), thumb-drive (1122),removable hard drive or solid state drive (1123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1100) can also include a network interface (1154) toone or more communication networks (1155). The one or more communicationnetworks (1155) can for example be wireless, wireline, optical. The oneor more communication networks (1155) can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of the one or more communication networks (1155) includelocal area networks such as Ethernet, wireless LANs, cellular networksto include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1149) (such as, for example USB ports of thecomputer system (1100)); others are commonly integrated into the core ofthe computer system (1100) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1100) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1140) of thecomputer system (1100).

The core (1140) can include one or more Central Processing Units (CPU)(1141), Graphics Processing Units (GPU) (1142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1143), hardware accelerators for certain tasks (1144), and so forth.These devices, along with Read-only memory (ROM) (1145), Random-accessmemory (1146), internal mass storage (1147) such as internal non-useraccessible hard drives, SSDs, and the like, may be connected through thesystem bus (1148). In some computer systems, the system bus (1148) canbe accessible in the form of one or more physical plugs to enableextensions by additional CPUs, GPU, and the like. The peripheral devicescan be attached either directly to the core's system bus (1148), orthrough a peripheral bus (1149). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1145) or RAM (1146). Transitional data can be also be stored in RAM(1146), whereas permanent data can be stored for example, in theinternal mass storage (1147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1141), GPU (1142), massstorage (1147), ROM (1145), RAM (1146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1100), and specifically the core (1140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1140) that are of non-transitorynature, such as core-internal mass storage (1147) or ROM (1145). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1140). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1140) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1146) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1144)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS AMVP: Advanced Motion Vector Prediction ASIC:Application-Specific Integrated Circuit ATMVP: Alternative/AdvancedTemporal Motion Vector Prediction BMS: Benchmark Set BV: Block VectorCANBus: Controller Area Network Bus CB: Coding Block CD: Compact DiscCPR: Current Picture Referencing CPUs: Central Processing Units CRT:Cathode Ray Tube CTBs: Coding Tree Blocks CTUs: Coding Tree Units CU:Coding Unit DPB: Decoder Picture Buffer DVD: Digital Video Disc FPGA:Field Programmable Gate Areas JCCR: Joint CbCr Residual Coding GOPs:Groups of Pictures GPUs: Graphics Processing Units

GSM: Global System for Mobile communications

HEVC: High Efficiency Video Coding HRD: Hypothetical Reference DecoderIBC: Intra Block Copy IC: Integrated Circuit JEM: Joint ExplorationModel LAN: Local Area Network LCD: Liquid-Crystal Display LTE: Long-TermEvolution MV: Motion Vector OLED: Organic Light-Emitting Diode PBs:Prediction Blocks PCI: Peripheral Component Interconnect PLD:Programmable Logic Device PUs: Prediction Units RAM: Random AccessMemory ROM: Read-Only Memory SCC: Screen Content Coding SEI:Supplementary Enhancement Information SNR: Signal Noise Ratio SSD:Solid-state Drive TUs: Transform Units USB: Universal Serial Bus VUI:Video Usability Information VVC: Versatile Video Coding

What is claimed is:
 1. A method of video decoding in a decoder,comprising: decoding prediction information for a current block in acurrent picture that is a part of a coded video sequence, the predictioninformation including a first syntax element indicating whether bothquantization parameter (QP) information of a luma component and QPinformation of a chroma component of the current block are included inthe prediction information; determining a QP of the chroma componentbased on the QP information of the luma component and the QP informationof the chroma component based on the first syntax element indicatingthat both the QP information of the luma component and the QPinformation of the chroma component are included in the predictioninformation; and reconstructing the current block based on the QP of thechroma component.
 2. The method of claim 1, wherein the QP informationof the chroma component is included in a picture header of the currentpicture based on the first syntax element in the prediction informationindicating that both the QP information of the luma component and the QPinformation of the chroma component are included in the picture headerof the current picture.
 3. The method of claim 1, wherein the QPinformation of the chroma component is included in a picture header ofthe current picture based on a second syntax element in the predictioninformation indicating that the current picture is not furtherpartitioned.
 4. The method of claim 1, wherein the QP information of thechroma component is included in a picture header of the current picturebased on a third syntax element in the prediction information indicatingthat the picture header of the current picture is included in a sliceheader of the current picture.
 5. The method of claim 1, furthercomprising: decoding a fourth syntax element in the predictioninformation indicating whether a QP of the luma component is equal tothe QP of the chroma component of the current block based on the firstsyntax element indicating that the QP information of the chromacomponent is not included in the prediction information; and determiningthe QP of the chroma component according to a luma-to-chroma QP mappingtable based on the fourth syntax element in the prediction informationindicating that the QP of the luma component is not equal to the QP ofthe chroma component of the current block.
 6. The method of claim 5,further comprising: determining the QP of the luma component as the QPof the chroma component based on the fourth syntax element indicatingthat the QP of the luma component is equal to the QP of the chromacomponent of the current block.
 7. The method of claim 5, wherein theluma-to-chroma QP mapping table is included in the predictioninformation.
 8. An apparatus, comprising processing circuitry configuredto: decode prediction information for a current block in a currentpicture that is a part of a coded video sequence, the predictioninformation including a first syntax element indicating whether bothquantization parameter (QP) information of a luma component and QPinformation of a chroma component of the current block are included inthe prediction information; determine a QP of the chroma component basedon the QP information of the luma component and the QP information ofthe chroma component based on the first syntax element indicating thatboth the QP information of the luma component and the QP information ofthe chroma component are included in the prediction information; andreconstruct the current block based on the QP of the chroma component.9. The apparatus of claim 8, wherein the QP information of the chromacomponent is included in a picture header of the current picture basedon the first syntax element in the prediction information indicatingthat both the QP information of the luma component and the QPinformation of the chroma component are included in the picture headerof the current picture.
 10. The apparatus of claim 8, wherein the QPinformation of the chroma component is included in a picture header ofthe current picture based on a second syntax element in the predictioninformation indicating that the current picture is not furtherpartitioned.
 11. The apparatus of claim 8, wherein the QP information ofthe chroma component is included in a picture header of the currentpicture based on a third syntax element in the prediction informationindicating that the picture header of the current picture is included ina slice header of the current picture.
 12. The apparatus of claim 8,wherein the processing circuitry is further configured to: decode afourth syntax element in the prediction information indicating whether aQP of the luma component is equal to the QP of the chroma component ofthe current block based on the first syntax element indicating that theQP information of the chroma component is not included in the predictioninformation; and determine the QP of the chroma component according to aluma-to-chroma QP mapping table based on the fourth syntax element inthe prediction information indicating that the QP of the luma componentis not equal to the QP of the chroma component of the current block. 13.The apparatus of claim 12, wherein the processing circuitry is furtherconfigured to: determine the QP of the luma component as the QP of thechroma component based on the fourth syntax element indicating that theQP of the luma component is equal to the QP of the chroma component ofthe current block.
 14. The apparatus of claim 12, wherein theluma-to-chroma QP mapping table is included in the predictioninformation.
 15. A non-transitory computer-readable storage mediumstoring instructions executable by at least one processor to perform:decoding prediction information for a current block in a current picturethat is a part of a coded video sequence, the prediction informationincluding a first syntax element indicating whether both quantizationparameter (QP) information of a luma component and QP information of achroma component of the current block are included in the predictioninformation; determining a QP of the chroma component based on the QPinformation of the luma component and the QP information of the chromacomponent based on the first syntax element indicating that both the QPinformation of the luma component and the QP information of the chromacomponent are included in the prediction information; and reconstructingthe current block based on the QP of the chroma component.
 16. Thenon-transitory computer-readable storage medium of claim 15, wherein theQP information of the chroma component is included in a picture headerof the current picture based on the first syntax element in theprediction information indicating that both the QP information of theluma component and the QP information of the chroma component areincluded in the picture header of the current picture.
 17. Thenon-transitory computer-readable storage medium of claim 15, wherein theQP information of the chroma component is included in a picture headerof the current picture based on a second syntax element in theprediction information indicating that the current picture is notfurther partitioned.
 18. The non-transitory computer-readable storagemedium of claim 15, wherein the QP information of the chroma componentis included in a picture header of the current picture based on a thirdsyntax element in the prediction information indicating that the pictureheader of the current picture is included in a slice header of thecurrent picture.
 19. The non-transitory computer-readable storage mediumof claim 1, wherein the stored instructions further cause the at leastone processor perform: decoding a fourth syntax element in theprediction information indicating whether a QP of the luma component isequal to the QP of the chroma component of the current block based onthe first syntax element indicating that the QP information of thechroma component is not included in the prediction information; anddetermining the QP of the chroma component according to a luma-to-chromaQP mapping table based on the fourth syntax element in the predictioninformation indicating that the QP of the luma component is not equal tothe QP of the chroma component of the current block.
 20. Thenon-transitory computer-readable storage medium of claim 19, wherein thestored instructions further cause the at least one processor to perform:determining the QP of the luma component as the QP of the chromacomponent based on the fourth syntax element indicating that the QP ofthe luma component is equal to the QP of the chroma component of thecurrent block.